A so-called double-Gauss type lens system has been used as a lens system used for an interchangeable lens for a single-lens reflex camera and a photocopy lens, and a lot of lens systems have been proposed in such as Japanese Patent Application Laid-Open No. 2007-333790.
However, a conventional double-Gauss type lens system generates large coma, so that it does not have sufficiently high optical performance.